Pine-spruce forests are one of the commonest mixed forest types in Europe and both tree species are very important for wood supply. This study summarized nine European studies with Scots pine and Norway spruce where a mixed-species stand and both monocultures were located in an experimental set-up. Overyielding (where growth of a mixed stand was greater than the average of both monocultures) was relatively common and often ranged between 0% and 30%, but could also be negative at individual study sites. Each individual site demonstrated consistent patterns of the mixing effect over different measurement periods. Transgressive overyielding (where the mixed-species stand was more productive than either of the monocultures) was found at three study sites, while a monoculture was more productive on the other sites. Large variation between study sites indicated that the existing experiments do not fully represent the extensive region where this mixed pine-spruce forest can occur. Pooled increment data displayed a negative influence of latitude and stand age on the mixing effect of those tree species in forests younger than 70 years.

A model was developed for predicting site index (SI) values and top height growth of lodgepole pine in northern Sweden. Data on 169 experimental plots from 61 experiments were used for model construction. Six dynamic site equations derived using the generalized algebraic difference approach (GADA) were tested. All of the equations estimate height and SI values on the basis of a known height and total age, and are base-age invariant. Unbiased parameter estimates were obtained by non-linear modelling without accounting for autocorrelation of residuals. The special formulation of the Hossfeld model and the GADA-transformed logistic function produced the most reliable SI curves. The Hossfeld model is recommended as it did not produce extreme outlying estimates for young stands. The developed model is polymorphic with variable asymptotes and can predict SI and dominant height growth for lodgepole pine between 20 and 50 years old.

The objective of this study was to compare volume growth and external timber quality properties of lodgepole pine (Pinus contorta Dougl. var. latifolia) stands planted in different spacings (1.41 X 1.41, 2.00 X 2.00, 2.83 X 2.83, 4.00 X 4.00) in southern Sweden. In northern Sweden lodgepole pine has been grown for a long time and shows superior volume production compared to Scots pine (Pinus Sylvestris L.). The Swedish Forestry Act restricts establishment of lodgepole pine plantations in southern Sweden. However, it is important to increase the knowledge about lodgepole pine and its potential use also in this part of the country. Two experiments in southern Sweden were studied. Each trial was designed as a random block experiment with two blocks. Both investigated stands had an age of 23 years at the time of assessment. The mean diameter and the volume production differed significantly between the spacings. The highest volume production was found in the narrowest spacing, 313% compared to the widest spacing. Significant differences between spacings were also found concerning external quality traits. The frequency of dominant and co-dominant trees without defects was 24% in the most open spacing compared to 46% in the narrowest one. Under current circumstances approximately 2500 seedlings/ha in the initial stand seems to be a reasonable compromise between growth, diameter development and timber quality.

In a stand with planted Norway spruce (Picea abies (L.) Karst.) and naturally regenerated birch (Betula pendula Roth and B. pubescens Ehrh.) in southern Sweden, the proportion of birch was reduced in 0.1-ha plots at pre-commercial thinning to 0%, 20% or 50% of the total stem number (2000-2500 stems ha(-1) after the thinning). The growth of both species was surveyed 4 and 10 years later. No significant between-treatment differences were observed on either occasion in total yield or in spruce diameter (apart from a more negative skewness of the diameter distribution of Norway spruce in the mixture with 50% birch compared to pure spruce). Birch retained its initial advantage in dominant height (of about 2 m) throughout the 10-year measurement period; hence, height growth rates of Norway spruce and birch were very similar. After three, four and 10 growing seasons, whipping damage to Norway spruce caused by birch was registered in the 20% and 50% birch mixtures, in which the proportions of damaged spruces were found to be similar, with 17% and 15% of damaged trees at the last inventory, respectively. In addition, simulations of the stands' development from the time of the last measurement until final felling at a total age of 66 years indicated that growth, yield and net present value decrease with increasing birch proportion, but if the proportion of birch removed in subsequent thinnings is increased, the between-treatment differences are reduced.

The effect of thinning intensity, thinning interval, thinning form and timing of the first thinning on stand level gross- andnet stem volume production in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst) was investigatedin a nationwide field experiment across Sweden. In total, 35 Scots pine sites distributed from the south to the north ofSweden and 13 Norway spruce sites located in the south and central parts of Sweden were investigated. Thinning treatments ranged from unthinned control, to light and moderate repeated thinnings, to a treatmentwhere 60-70% of the basal area was removed in a single thinning. In addition, thinning from above was compared tothinning from below and delayed first thinning was compared to early first thinning. The average measurement period was31 years for Scots pine and 30 years for Norway spruce. All Scots pine thinning treatments reduced the total gross stemvolume production compared to the unthinned control, whereas only the heaviest thinning treatments, in which a largeproportion of the basal area was removed, reduced the total gross stem volume production for Norway spruce. Thinningfrom above did not affect total gross stem volume production of Scots pine, but there was a tendency towards lowerproduction in Norway spruce. For Norway spruce, thinning from above resulted in lower net stem volume production thanthinning from below. Delaying the first thinning did not affect gross stem volume production for either Scots pine orNorway spruce. Net volume production and volume production in trees with diameter at breast height > 8 cm was higher forthe light thinning treatment than for the unthinned control in Norway spruce. In Scots pine, there was no differencebetween the light thinning treatment and unthinned control in net volume production. For cots pine, the heavy thinningtreatments decreased net volume production compared to the unthinned threatment whereas there were no differences innet volume production between the heavy thinning treatments and unthinned control in Norway spruce.

We review and discuss the applicability of mixed stands in the context of sustainable forestry in southern Sweden. This is done from a silvicultural perspective regarding aspects such as regeneration, pre-commer-cial thinnings, production, economy, damage and policy implications. The paper is based on literature reviews and on studies performed in southern Sweden or under comparable conditions. After considering the underlying mechanisms, we find that it is possible to establish a mixed stand in the regeneration phase and sometimes even to a lower cost compared to monocultures. To keep the mixture, or to create it, with pre-commercial thinnings is, however, often more expensive. The reviewed studies, together with a new simulation, show that the effect on productivity of mixed stands compared to monocultures is minor. Some positive effects on damage (i.e., decreased levels) in mixed stands have been found. The economy and the policy implications of mixed stand management were found to be dependent on the specific stand and situations. A general finding was that research and knowledge of managing mixed stands, as compared to monocultures, are limited, which in turn could limit the applicability of mixed stand management.

The development of different stand structures, including Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth), were simulated from the time of precommercial thinning until the dominant height of spruce reached 13m. The aim was to find a combination of Norway spruce and silver birch that ensured a satisfactory development of spruce combined with a long-term admixture with birch. Empirical models were used to create initial stands and to estimate the growth of the individual trees. The initial number of stems was 2500ha−1 and the proportion of birch was 0, 20, 40 and 60%. The initial average height of Norway spruce was set to 3m and for birch the height was varied between 1–6m. Conditions describing a medium fertility in southern Sweden was used in the simulations. In mixtures with the greatest initial birch height, the total volume after 15 years was similar to or greater than in a monoculture of Norway spruce with 2500 stems ha−1. The total volume was greater in mixtures compare to Norway spruce monocultures of the same density as the spruce component in the mixtures. The volume of Norway spruce decreased with increasing initial birch height if the average height of birch exceeded 2m. The status of competitive birches at the time of first commercial thinning was identified by investigating variables describing vital birches in a survey study. Given the conditions used in this study, it was concluded that leaving birch with an average height slightly greater (0.5–1m) than that of spruce after precommercial thinning will result in a large number of competitive birches at first commercial thinning. It was also indicated that the dimensions of the Norway spruce will be similar to a monoculture of Norway spruce with 2500stemsha−1. When the initial average height of birch exceeded 4m the increase in the number of competitive birches leveled off due to intra-species competition.

The natural regeneration of beech (Fagus sylvatica) was studied under various shelterwood densities and soil preparations in a 130-year-old beech stand in southern Sweden. Between 1990 and 1996, seedling emergence, survival, growth and damage were followed in a clear-cut and in two shelterwoods with different densities, in plots with undisturbed ground, bare mineral soil or ridges with mineral soil on top of humus. Irradiation, soil and air temperatures, soil moisture and precipitation were continuously recorded during the first three growing seasons. The seedling emergence was higher in the shelterwoods than in the clear-cut. The mortality was the highest during the first year. The seedling number was the highest on bare mineral soil and the lowest on undisturbed ground, for all cutting regimes. The increase in seedling height and dry mass was greater in the clear-cut and in the sparse shelterwood than in the dense shelterwood. Damage due to frost was more frequent in the clear-cut than in the shelterwoods. Effects of most kind of damage had only minor influence on the seedling height, whereas in seedlings experiencing frequent damage height was reduced.

Experimental growth data collected over 20 yrs were used to assess volume increment and yield in mixed and monoculture stands with Scots pine and Norway spruce. Differences in volume increment were generally small between the different types of stand, indicating that there is little to be gained in total volume increment from using mixed stands with Norway spruce and Scots pine instead of monocultures on sites with medium fertility. However, since the volume increment of pine per unit area was higher in the mixture than in the monoculture, the results indicate that retaining some Norway spruce in Scots pine stands would result in an increase in the total volume increment. The diameter of the Scots pine was 1.2 cm greater in the mixture than in the monoculture at the end of the observation period. There was no layering on the plots, but the Scots pine trees were slightly taller and thicker than the spruce. The Scots pine stems tapered more in the mixture than in the monoculture. Stem defects were not consistently different between the stand types. The diameter distribution of the total tree population in the mixture was less tightly clustered round the mean than in the monocultures. Research designed to identify ways to increase the total volume increments using mixed stands should probably focus on mixtures of species that differ more in growth patterns than Scots pine and Norway spruce apparently do.

A study was undertaken to evaluate the effect of Scots pine (Pinus sylvestris) shelterwood density and timing of removal on the regeneration of forests with improved wood quality. This paper focuses on the effect of scarification and seedfall on the success of natural regeneration of Scots pine under two shelterwood densities and in a clear-cut. Wood quality aspects will be addressed later in the study. After 4 yrs, natural regeneration of Scots pine under a 200 stems ha(-1) shelterwood reached 90000 seedlings ha(-1), 53000 under a 160 stems ha(-1) shelterwood and 3700 in a clear-cut. The high natural regeneration under the densest shelterwood resulted from a high seedfall, slower invasion by competing vegetation, consequent prolonged recruitment and low mortality. Since mortality largely decreased for both shelterwood densities and recruitment seems to continue, the success of regeneration should be maintained in the future if proper release operations are conducted. The latter could begin when seedlings reach a height of about 0.5 m and the cover should be maintained until they reach a height of about 6 m. Therefore, it may be possible to use 200 stems ha(-1) Scots pine shelterwoods in southern Sweden to obtain dense stands and thus improve wood quality (stem taper, wood density, etc.).

Timber quality in Scots pine (Pinus sylvestris L.) stands in Sweden has deteriorated during the 20th century. A possible cause of this is the increasing proportion of timber that originates in planted stands. Two naturally regenerated and two planted pine stands, of the same genetic origin, were compared. The planted stands were established as spacing experiments (1.25 x 1.25-2.5 x 2.5 m) at Tonnersjoheden Experimental Forest (lat. 5642'N, long.l306'E, alt. 60 m). Volume growth and timber quality, i.e. taper, crookedness, number of branches, branch thickness, branch angle, crown size, occurrence of spike knots and damage were compared. The quality of dominant and co-dominant trees was higher in the naturally regenerated stands than in the planted stands. Of the planted trees, only 25% were straight, compared with 86% of naturally regenerated trees. In the planted stands, the mean diameter of the thickest branch below 2 m was 23 mm, compared to 15 mm in the naturally regenerated stands. Timber quality and planting density were also positively correlated, quality being very poor at the widest spacings. Volume growth at initial spacings of 1.75 x 1.75 m and denser was estimated to be 5-10% higher than that in the naturally regenerated stands.

An empirical model is presented to forecast the incidence of root rot at stand level. In addition, the impact of different thinning programmes on the incidence of root rot is evaluated. The model is based on data from 152 permanent forest research plots of pure Picea abies in southern Sweden, within which the incidence of root rot at stump height in thinned trees has been recorded after each thinning since 1950. In total, about 20 000 stumps have been studied. According to simulations with the model, areas previously used as fields or for grazing are particularly susceptible to root rot, while old hardwood sites are less susceptible. Furthermore, simulations with the model imply that the earlier, the harder or more often a stand is thinned, the faster will be the development of root rot.